LIGHT VERSION
The MOD-KITs of the ULTRAGRIP COLLECTION come with a smaller 150mAh battery. You don't have to use it though! Have fun building.
For disassembly, check out this video:
https://www.youtube.com/watch?v=wfK_26Ey7N0
Click the video below for the instructions
Check the Side button PCB
Some PCB versions have an extension which makes it impossible to add to the shell. The solution is to remove the green/yellow sticker with an Xacto knife or a pair of scissors.